The region of electromagnetic spectrum lying in the giga (GHz)-terahertz (THz) frequency range has recently become of increasing interest in the various fields of science and technology. In part, such interest is caused by unique properties of GHz-THz radiation, which make such radiation appealing for a great number of useful applications. Terahertz radiation is non-ionizing, and thus, unlike X-rays, it is not harmful for biological tissues and DNA. In addition, most biological and chemical agents have resonant absorption lines in the THz region. Therefore, accurate and safe tomography of different human and other biological tissues may be enabled. Because terahertz radiation can penetrate fabrics and plastics, it can be used in security applications, e.g., to screen for concealed weapons. The high-frequency nature of the THz radiation makes it possible to utilize it in higher frequency computer and high-altitude telecommunication systems. Likewise, terahertz sensing and imaging may be used in many applications in the field of manufacturing, quality control and process monitoring. These applications generally take advantage of the properties of plastics, cardboard and other packaging materials being transparent to terahertz radiation, and thereby making it possible to inspect packaged products. Similarly, THz radiation affords additional tools of scientific research in a variety of fields, from submillimeter and millimeter astronomy investigations to solid state research.